Loops and Logic - Beginning Java 2 SDK - page 76

This provides an explicit choice between two courses of action - one for when the if expression is
true and another for when it is false .
We can apply this in a console program and try out the random() method from the Math class at the
same time.
Try It Out - if-else
When you have entered the program text, save it in a file called NumberCheck.java . Compile it and
then run it a few times to see what results you get.
public class NumberCheck {
public static void main(String[] args) {
int number = 0;
number = 1+(int)(100*Math.random()); // Get a random integer between 1 & 100
if(number%2 == 0) { // Test if it is even
System.out.println("You have got an even number, " + number); // It is even
} else {
System.out.println("You have got an odd number, " + number); // It is odd
}
}
}
How It Works
We saw the method random() in the standard class Math in the previous chapter. It returns a random
value of type double between 0.0 and 1.0, but the result is always less than 1.0, so the largest number
you will get is 0.9999... (with the number of recurring digits being limited to the maximum number that
the type double will allow, of course). Consequently, when we multiply the value returned by 100.0
and convert this value to type int with the explicit cast, we discard any fractional part of the number
and produce a random integer between 0 and 99. Adding 1 to this will result in a random integer
between 1 and 100, which we store in the variable number . We then generate the program output in
the if statement. If the value of number is even, the first println() call is executed, otherwise the
second println() call in the else clause is executed.
Note the use of indentation here. It is evident that main() is within the class definition, and the code
for main() is clearly distinguished. You can also see immediately which statement is executed when
the if expression is true , and which applies when it is false .
Nested if Statements
The statement that is executed when an if expression is true can be another if , as can the statement
in an else clause. This will enable you to express such convoluted logic as "if my bank balance is
healthy then I will buy the car if I have my check topic with me, else I will buy the car if I can get a
loan from the bank". An if statement that is nested inside another can also itself contain a nested if .
You can continue nesting if s one inside the other like this for as long as you still know what you are
doing - or even beyond if you enjoy confusion.
To illustrate the nested if statement, we can modify the if from the previous example: